Brush assembly for dynamoelectric machines



June 6, 1944. 1 c. PRATT 2,350,968

BRUSH ASSEMBLY FOR DYNAMOELECTRIC MACHINES Filed July l0, 1942 14 i n' f/4 I Paiented'June 6, 1944 2.35am pausa 'assuma ron nrumomcmo nscnmss Leonard C. Pratt,

Singer Manufacturing N. J.. a corporation of New Jersey Application Jllly Il. 1942. Serial No. 450,418

13 Claims. (Cl. 171423),"

'I'his invention relates to a brush assembly for conducting electric currents between stationary and rotating'elements of dynamo electric machines.

More especially, the invention relates to an improved brush assembly comprising brushes, brush supports and an insulated base forming a unitary structure which may be readily assembled into or removed from the dynamo electric machine.

The brush structure herein disclosed may be used alternatively with that shown and described in the copending U. 8. patent application Serial No. 436,992 o! Fuge. et al. filed March'31, 1942.

In small dynamo electric machines of the type referred to in the trade as Selsyns, Autosyns, etc., and used in so-called synchro-tie or self-synchronous systems for transmitting angular position indication between mutually remote points. a peculiar problem arises in connection with rotor current collection due to the special nature and use of these devices which will now be described. These units are ordinarily used in pairs connected together electrically, one unit, called a transmitter being placed at a given location for sending out the indication, and a second similar unit, called a receiver being placed at a remote location for receiving the indication. It is important that the receiver" duplicate the movement of the transmitter" as closely as possible in order to provide suillcient accuracy of indication. It has been found that any resistance offered to the rotation of the "receiver rotor adversely affects the accuracy of indication of the system. Primarily, this resistance is made up of bearing friction and brush friction which, of course, are always present 'to some degree. The bearing friction is minimized by the use of precision ball-bearings. Attempts to reduce the brush friction by modification oi' the usual brush structure employing r a di a l spring-pressed brushes have not met with much success. For example, merely to reduce the spring pressure with which a radial brush is held against its slip ring does not improve the current-collecting function of the combination because this reduction in pressure renders the brush mechanically unstable and liable to be jarred out of contact with the slip ring, thus opening the circuit to the rotor and producing erratic and false indications at the receiver.

One object of the invention, therefore is to provide a novel brush assembly in which light spring wires supported on conducting posts,

, Elinbeth,

which are embedded in a base of molded insulation material, are bent so as to form resilient loops and to present two angularly separated limbs for contacting current-collecting slip rings at different points with a steady but light resilient pressure to insure proper and reliable current collection with minimum frictional torque resisting the rotation of the rotor.

A further object of the invention is to provide a brush assembly which may be readily removed as a unit from or replaced on adynamo electric machine, including provision for insuring the proper axial alignment of the slip rings with the brushes.

I have constructed a brush assembly in accordance with this invention adapted to make contact with slip rings having a diameter of approximately one-quarter of one inch, a face width of about one-sixteenth of an inch, and an axial separation of about one-sixteenth of an inch. It is evident from these dimensions that the clearances and spacing of the parts must be made small with vallowance for adequate separation and proper arrangement for safe insulation between brushes.

With the above and other objects in view, as will' hereinafterappear, the invention comprises the combination and arrangement of parts hereinafter set forth and illustrated in the accompanying drawing of a specific embodiment of the invention from which the several features of the invention and the advantages attained thereby will be readily understood by those skilled in the art;

In the accompanying drawing- Fig. 1 is a longitudinal sectional view through a dynamo electric machine having a brush assembly embodying the invention.

Fig. 2 is a transverse sectional view taken substantially on the line 2 2 of Fig. 1.

Fig. '3 is a top plan view partly in section, of the brush assembly shown in Fig. l.

Fig. 4 is a bottom plan view of the brush assembly of Fig. 1.

Fig. 5 is a perspective view of the brush assembly of Fig. l.

Referring more particularly to the drawing. Fig. 1 shows a dynamo electric machine having a stator-structure comprising a die-cast stator frame I, a magnetic stator core 2 carried by said frame, a stator current-carrying-winding 3 received by the stator core, a non-magnetic endbonnet I secured to the stator frame I, by bolts I; and a ball-bearing 6 carried within a bore in the end-bonnet 4.

The rotor structure comprises a shaft 'I car-r' ried at one end by the ball-bearing l, a magnetic core 8 ilxed on said shaft, a current-carrying winding 9 received by said core and current-conducting slip-rings I0, carried by the shaft and insulated from each other and from the shaft, and connected electrically to the winding 3.

This dynamo electric machine structure is more completely disclosed in the copending application Serial No. 432,384, of William H. Brady, filed February 26, 1942, to which reference may be had.

The end-bonnet 4 is formed with an-opening II between flattened inturned wall portions I2 which form a seat for a wafer-like supporting block I3 secured to said end-bonnet 4 by means of screws I4 extending through apertures in said block and threaded into said wall portions I2. Made preferably of molded insulating material, the supporting block I3 is formed on the exterior with a generally cylindrical surface which conforms to the peripheral contour of the endbonnet 4, except where flat portions are provided for seating the screws I4. Within the endbonnet 4, the block I3 presents a flat supporting platform surface I5 located in a plane normal to a radial plane through the center of the apertured portion II.

Post members I6, having sufficient electrical conductivity, are formed at one end with a knurled cylindrical portion I1 which is securely embedded in the block I3 to anchor said post members I6 therein. As shown most clearly in Fig. 5, the post members rise from the block I3 and stand perpendicular to the platform surface I5, spaced apart equidistantly from and on either side of a radial plane through the center of the apertured portion. Furthermore, the post members I6 are spaced apart axially to coextend with the similar spacing of the slip rings, as seen best in Fig. 3. At their free ends, the post members are each provided with a transversely slotted portion I8 occupying approximately one-fourth the length of the post members. A light spring wire brush-member I9 of corrosion-resistant material and having a circular cross-section is first bent to form a hair-pin loop having two limbs which are passed through vertically spaced apart transverse apertures in the post members from the inside or mutually proximate faces tothe outside faces thereof, and the heads of the loops are soldered, brazed or similarly secured to the post members at the loop end 2I, to form two cantilever beam members. The limbs are then bent back from the outside, are guided within the slotted portion I8, and extend inwardly and upwardly to diverge at their free ends and to embrace the slip-rings III, as clearly seen in Fig. 2. In the operative position, the limbs of each single-wire brush are sprung apart at an acute angle to receive the associated slip-ring so as to tangentially contact said slip ring at two separated points on the periphery thereof. The chordal distance subtended between the points of contact on the slip rings I0 is greater than the linear distance between the points of contact on the unsprung limbs of wires I9 so that the limbs must be sprung apart to engage the slip rings in contacting relation, thus providing the requisite radial pressure, derived from the resilience of the wire itself, for holding said limbs against said slip rings.

The axially adjacent brushes have an angular separation of substantially 90 degrees. This permits sufllcient swaration between the post members I6 for adequate insulating eilect with allowance for maintaining the nearly vertical brush limbs at such a position relative to the slip rings that said limbs are deflected outwardly to permit entry of the slip rings within the angle of the brush limbs when the brush assembly is inserted radially within the end-bonnet 4.

I'he free end portions 22 of the limbs of the wire brushes I8 are bent outwardly on a smallradius to facilitate the assembly of the unitary brush structure into the end-bonnet by providing guides for properly leading the limbs of the brush over the periphery of the slip rings. This is of special importance in this case where the brush assembly, as shown in Fig. 5, includes a closure element (the block I3), which when xed in place renders the brushes inaccessible for an? subsequent adiustment relative to the slip rings.

The supporting block I3 has depressed slot portions 23 disposed axially in the inner surface for receiving and protectively guiding the insulated leads 24, within the end-bonnet 4 where they are electrically connected at 25, by means of soldering, or other suitable means, to the embedded cylindrical portions I'I of the post member I5 whereby to supply the rotor winding with current from external sources.

From the foregoing description it is clear that the block I3 serves as: (1) a mechanical support for the brushes, (2) a terminal block for the connection of leads for supplying current to the rotor and (3) a removable closure for completing a substantially dust-tight enclosure for the rotor.

The slotted portions I8 of the post members I6 provide vguideways for the wire brush limbs to limit their axial displacement so that the brushes are maintained in contact with the slip rings and at the same time are permitted substantially unrestricted displacement in planes transverse to the rotor axis. The loops formed by bending the wire limbs back through the slotted portion provide considerable resilience in the brush for de ilection in directions transverse to the rotor axis and substantially in the median plane of the slip rings. In order to provide brushes which will respond readily to and follow closely any changes in the surface contours of the slip rings to maintain continuous electrical contact therewith, lightness of weight is combined with the resilience mentioned hereinabove.

I have found that a small spring wire provides the right proportion of these components of weight and resilience and also provides suillcient electrical conductance for the rotor current. Further, the cylindrical surface of the brush limb, when pressed against the cylindrical surface of the slip ring according to the invention, forms a contact of very small area which minimizes the total brush frictional force and the resisting torque Produced by it. Further, the small area of sin'face contact between brush limb and slip ring allows sufficient intensities of contact pressure to secure a low contact resistance loss and at the same time keeps the total pressure suiiiciently low to avoid an adversely large frictional loss.

The double contact provided by each brush greatly increases the probability of maintaining a continuous electrical contact between brush and slip ring even though said brush and slip ring may have severe relative lateral displacements as may, for example be incidental to applications of these devices to aircraft, marine or land vehicles. This continuity of electrical connection is of particular importance with regard to the use of Selsyn type units for the transmission of navigational control data where discontinuities in and erratic behavior of the received indication cannot be safely tolerated.

From the above description it may be clearly seen that riveting and the use of special insulated washers, sleeves and the like, are entirely eliminated from the manufacture of this brush assembly. Further, it will be perceived that I have provided a compact, lightwelght, inexpensive and rugged unitary brush -assembly which may, by simple external manipulation, be attached to or withdrawn from the end-bonnet of a dynamo electric machine to eiIect sure and reliable external electrical connection or disconnection with the rotor winding.

It will be obvious'to those skilled in the art that the invention may, without departure from its essential attributes, be embodied in various specific forms other than that shown and described, which latter is to be considered in all respects as illustrative of the invention and not restrictive.

Having thus set forth the nature of the invention what I claim herein is:

1. A brush assemblyl for rotating dynamo electric machines having slip rings, comprising, in combination. a block structure having a platform portion, rigid current-conducting post members secured at one end to said block structure and extending in a direction substantially perpendic- .ular to and away from said platform portion,

spring wire brush members supported from said post members and having divergent limbs angularly spaced apart to embrace said slip rings in l resilient tangential contacting relation.

2. A unitary brush assembly for a rotating dynamo electric machine having slip rings, comprising a block of insulating material, electrical conducting post members erectly embedded at one end in said block and positioned in ilxed parallel spaced-apart relation, brush members of spring wire secured to said post members and each formed into a loop having divergent limbs forming the sides of an acute angle within which is positioned one of said slip rings in resilient tangential contacting relation with said wire limbs.

3. In a dynamo electric machine having a casing with an aperture and a rotor which carries current-conducting means; a unitary brush assembly comprising a base removably secured to said casing to cover said aperture, current-conducting post members secured to said base in erect spaced-apart relation, spring wire brush members secured to said post members and each formed into a bent loop having two limbs which diverge toward their free ends to form an angle within which said rotor current-conducting means is positioned and resiliently engaged in tangential surface contact with said divergent limbs.

4. In a dynamo electric machine having a casing, an aperture in said casing, and a rotor which carries current-conducting means; a unitary brush assembly comprising a base removably secured to said casing to cover said aperture, current-conducting post members secured to said base in erect spaced-apart relation, spring wire brush members ysecured to said post members and each formed 4into a-bent loop having two limbs which stand in a direction generally inward with respect to the post members and upward from the associated post member and which diverge toward their free ends to form an angle within which said rotor current-conducting means is positioned and resiliently engaged in tangential surface contact with said divergent limbs.

5. A brush assembly for rotating dynamo electric machines having a rotor provided with slip rings, comprising, in combination, a wafer-like block of molded insulation having a platform portion, rigid current-conducting post members embedded at one end in said block and extending in a direction vsubstantially-perpendicular to and away from said platform portion to form supporting studs symmetrically positioned relative to the axis of said rotor, spring wire brush members supported from said post members and having divergent limbs angularly spaced apart and bent inwardly relative to the .post members and upwardly from said respective post members to embrace said slip rings in resilient tangential contacting relation.

6. A brush assembly for a rotating dynamo electric machine having slip rings. comprising a wafer-shaped insulated base member having a platform portion, rigid current-conducting post members secured at one end to said base member and provided at the remote end thereof with a slotted portion extending in a direction substantially perpendicular to and away from said platform portion, spring wire brush members supported from said post, engaged by said slotted portion and having divergent resilient limb p0rtions of cylindrical formv spaced apart at an acute angle to embrace the slip rings, said slotted portion of the post members providing guide means positioned to conilne the displacement of said limb portions substantially to the median planes of said respective slip rings.

7. A unitary brush assembly for a rotating dynamo electric machine having a rotor which carries current-conducting means, comprising a wafer-like block of insulating material, electrical conducting post members, each erectly embedded at one end in said block to stand in xed parallel spaced-apart relation and formed at the free end with a slotted portion, brush members of spring wire, each secured to one of said post members and formed into a bent loop having spaced-apart limbs which are received within said slotted end portion and coniined thereby to limited lateral movement, said limbs being extended beyond said slotted portion to form divergent angularly spaced apart contacting members in resilient tangential contact with said rotor current conducting means.

8. A brush assembly for rotating dynamo electric machines having slip rings, comprising, in combination, a block of insulating material having a flat platform portion, straight rigid currentconducting post members provided with transverse apertures and secured at one end to said block and formed at the other end with slots extending in a direction substantially perpendicular to and away from said platform portion, spring wire brush members secured to said post members and having opposed limbs which extend through the apertures in said post members and are bent upwardly along the post members and then reversely through said slots to terminate in angularly spaced apart portions which diverge towards their free ends to embrace said ilip rings in resilient tangential contacting rela- 9. In a dynamo electric machine having a casing, an aperture in said casing, and a rotor which carries slip rings; a unitary brush assembly comprising a base removably secured to said casing to cover said aperture, current-conducting post members extending inwardly from said'basetoward said slip rings. said post members being grecs.

l0. A unitary brush assembly for a rotating dynamo electric machine having a casing with an aperture and a rotor with current-conducting means, comprising insulated base means removably secured to said casing to cover said aperture, electrical conducting supporting means secured to said base means, brush means including limbs of light spring wire having ends nxed in said supporting means to form cantilever beams which are bent to diverge from each other toward their free ends and to form an angle within which said current; conducting means is positioned and reslliently engaged in tangential surface contact by said divergent limbs.

11. A brush assembly for dynamo electric machines including, a supporting base, spaced post members extending from said base and each having a guide-slot, and brush members carried by the respective post members, said brush members each comprising spring wire limbs anchored to its respective post and reversely bent to extend through the guide-slot of its respective post member.

12. A brush assembly for dynamo electric machines including, a supporting base, spaced post members extending from said base and each provided with a pair of apertures and with a guide- 10 slot, and brush members carried by the respec- [tive post members. said brush members each com- ,prising a U-shaped spring wire having the limbs thereof disposed in the apertures and reversely bent to extend through the guide-slot of the same 15 post member.

13. A brush assembly for dynamo electric machines including, a supporting base. a pair or spaced post members extending from said base and each having a pair of apertures and a gulde- 20 slot, said apertures extending transversely and said guide-slot being elongated lengthwise of the post, and brush-members carried by each post and comprising a U-shaped spring wire having the limbs thereof extending through the aper- 25 tures of a post from the side thereof proximate to the other post, said limbs being reversely bent at the opposite side of the post to extend through the guide-slot of the same post.

LEONARD C. PRATT. 

